Spark plug tester



May 8, 1934. H. RABEZZANA ET AL SPARK PLUG TES TER Filed Oct. 428, 193550 shaft Patented May 8, 1934 PATENT OFI-ics UNTED STATES 1,957,803SPARK PLUGTESTER Hector Raben-rana. and Ralph L. Phelps, Flint, Mich.,assgnors to A C' Spark Plug Company,

Flint, Mich., a company of Michigan Application October 28, 1933, SerialNo. 695,578

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l with a shunt circuit to leak current from the spark plug circuit. Withsuch device, the brightness of the flasher will not be materiallyaiected by current leakage through the shunt if the spark plug is ringproperly. If, however, the ordinary operation of the plug is faulty theadditional current leakage through the tester shunt will cause a weakspark or else complete failure, and the dasher to some extent will becorrespondingly dimmed. Glowing of the neon tube results from highfrequency oscillations produced upon current discharge across the sparkgap of the plug, and its brightness varies in direct relation to thedifierential in potential at its opposite ends. With the constructionheretofore used, only one end of the tube is directly connected througha conductor with the secondary circuit of the ignition system, andconsequently, variations in flash intensity, while discernible to anexpert, are not pronounced to the untrained eye. It is now proposed toeliminate this uncertainty and to improve the reading and make moreapparent the differences between a spark plug firing regularly under anyload and one which misses only under sudden load. For this purpose theneon tube is placed in a wiring circuit so that both ends are connectedthrough conductors of the same capacity and resistance with the sparkplug terminal for the flow by induction oi the high frequency current.

For a better understanding of the invention, reference may be made tothe accompanying drawing, wherein Figure l shows a portion of aninternal combustion engine with the tester applied thereto. Figure 2 isa top plan view of the tester with parts in section, and Figure 3 is asectional View taken on line 3--3 of Figure 2. Figure l is a sideelevation partly in section, and Figure 5 is a diagrammatic view ci thewiring circuits involved..

Referring to the drawing, the box or casing 1 of bakelite or the like,has a depression in its top face to receive a pointer knob 2, carried ona 3 extending through the wall of the casing toward the removable bottomwallv fiA where it mounts a movable switch blade 5. The blade 5,isgrounded. through a springl contact nger 6 in wiping contact withthe'lower end of the shaft 3 and mounted on the wall of the-'casing byscrews which also connect thereto a length of exible cable 7.

Arranged about an arc, whose center is the shaft 3, are a series of fourhollow bosses 8--8, each of which receives a conductor element 9,preferably in the form of a carbon stick of a preselected resistance.One end of the carbon stick 9 seats within a thimble 10 having a roundednose to rest on the bottom wall of the casing, but adapted to makecontact with and seat between the split or forked ends oi the switchblade 5, when the blade is swung thereunder. V

The stick 9 -is pressed downwardly by a coiled compression spring 11 atits upper Aend within a cup 12 that bears against an arcuate conductorstrip or bus bar 13, extending over the several hollow bosses 9 5.

The bus bar 13 has a connection at 14, with a lead-in cable 15, and atits end is joined to a downwardly extending strip 16 that terminates inan upstanding tab 17 in the compartment that receives a neon tube 18. Anopening 19 with a, shad-4 ing shield 20 may be provided for theobservation oi the neon tube. interposed between the tab 17 and one endof the tube 18 is a coiled compression spring 21 which holds theopposite end of. the tube in contact with the lead-in wire 22. The twolead-in wires l5 and 22 are of the same resistance and capacity, andtheir outer ends are joined to a common clip for connection with a sparkplug terminal connector. Spacers 23 hold the two wires apart to preventinduction therebetween.

In the construction described, the switch blade 5 may be moved into anyone oi iive positions by the movement of the pointer knob 2 into aline-,ment with projections 24.0, 25, 26, 27 and 28 on the top face of thecasing. At any of the stations 25 to 28, inclusive, the switch bladegrounds the bus bar 13 through the conductance element 9 associated withthe particular station selected, while at station 24 the groundconnection is broken. Thus, when the device is in use, a shunt circuitwhich includes the cable 15, may be closed for current leakage iromtheignition system in amount depending upon the pointer setting, since theseveral conductance elements 9 are of different resistances. it isproposed, for example, that the difference in resistors should beapproximately 100,000 ohms, starting at about 270,000 ohms and ending'atabout 630,000 ,ohms resistance. This enables the one instrument to beused for testing practically all or the various types of engines used inautomobiles.

In the use of the device, the cables l5 and 22 are connected to thespark plug and the calici? is grounded at any convenient point on the`en gine, as is illustrated in Figurel. With this ar. rangement ofparts, the cable 15, in addition tof I forming a part of the shuntcircuit, also provides and with minimum resistance, the strength of theglow conforms to the character of the spark discharge. A

To determine probable plug life, a test is made with the pointer knobset at a given station for the particular type of engine and spark plug,with a conductance element of selected resistance in the shunt circuit.This allows leakage' of current from the ignition circuit andconsequently a drop in voltage at the spark gap. If the gap is of propersize and the leakage through fouling not great, then the leakage throughthe instrument will not be sflicient to'cause the plug to missA evenunder sudden load. Any irregular ring under test and which is radilydiscernible through a dimmingofthe neon tube indicates that the plugneeds cleaning and regapping or else complete replacement.

It should be noted that the plug is tested in the engine under actualrunning conditions and when the engine is normally hot. For an accuratereadinguthe flashes should be observed through-l out the entire range ofquick acceleration, and if it dimsv or disappears at any time, then theobserver is informed that the plug is missing and has reached its linutof economical performance. Should the tester indicate irregular firingwith a new plug, then trouble lies in other portions of the ignitionsystem which should be carefully checked.

We claim:

1. In a device for testing spark plugs while the engine is operating, apair of lead wires of substantially1 the, same capacity and resistanceadapted for connection with the spark plug circuit, a flasher actuatedby high frequency discharge connected at opposite ends with said leadwires to form therewith a closed circuit, and means to shunt currentfrom the spark plug including a conductance element having resistance ofa given value.

2. In a device for testing spark `plugs while the .engine is operating,a flasher operated by high frequency oscillations produced by thedischarge of current at the spark gap, a cable connecting one end of theflasher with the spark plug, a second cable substantially correspondingin resistance and capacity with the first cable and connecting theopposite end of the flasher with the spark plug, said cables and flashertogether constituting a closed circuit, and means including aconductance element of a'given resistance for shunting current from thespark gap.

3. A spark plug tester, including a support, a resistor element of agiven resistance value mounted in the support, means to ground saidelement, a neon tube carried by the support, a conductor element commonto said resistor element and one end of said neon tube and adapted forconnection with the spark plug circuit, and a second conductor ofsubstantially the same resistance and capacity as the first mentionedconductor, associated with the opposite end of the neon tube forconnection with thev spark plug circuit. I

4. A spark plug tester including a casing for a neon tube, a pair ofexible cables of substantially the .same resistance and capacity,extending from said casing, with their inner ends connected to theopposite ends of the neon tube, means for connecting the outer ends ofthe cable with the ignition circuit, and means spacing said cables `intermediate the ends thereof to eliminate induction of one over theother.

5. Means for testing the operating condition of a spark plug, includinga casing, a neon tube within the casing, a pair of cables extending from'the casing for connection at the outer ends with a spark plug and.having their inner ends connected to opposite ends of the neon tube toprovide a closed circuit for high frequency current ow,a conductanceelement within the casing, having a resistance of a predetermined value,a switch for grounding said element and means connecting said element toone of said cables and providing therewith a shunt circuit forby-passing current from the spark plug.

6. A device for testing spark plugs while the engine is operating,including a closed circuit containing a ilasher operated by highfrequency oscillations result' -g from current discharge at the sparkplug, and a shunt circuit for leaking current from the ignition system.

HECTOR RABEZZANA. RALPH L. PHELPS.

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